The Shark Bay region represents a meeting point of three major climatic regions and forms a transition zone between two major botanical provinces-the South West and Eremaean provinces.
The number of species that reach the end of their range is a major feature of the region's flora. Twenty-five per cent of vascular plants (283 species) are at the limits of their range in Shark Bay. Many vegetation formations and plant species are found only in the interzone area.
The area south of Freycinet Estuary contains the unique type of vegetation known as tree heath. There are also at least 51 species endemic to the region and others that are considered new to science.
The Shark Bay region is an area of major zoological importance, primarily due to habitats on peninsulas and islands being isolated from the disturbance that has occurred elsewhere. Of the 26 species of endangered Australian mammals, five are found on Bernier and Dorre Islands. These are the boodie or burrowing bettong, rufous hare wallaby, banded hare wallaby, the Shark Bay mouse and the western barred bandicoot.
The Shark Bay region has a rich avifauna with over 230 species, or 35 per cent, of Australia's bird species having been recorded. A number of birds attain their northern limit here, such as the regent parrot, western yellow robin, blue-breasted fairy wren and striated pardalote.
The region is also noted for the diversity of its amphibians and reptiles, supporting nearly 100 species. Again, many species are at the northern or southern limit of their range. The area is also significant for the variety of burrowing species, such as the sandhill frog, which, apparently, needs no surface water. Shark Bay contains three endemic sand swimming skinks, and 10 of the 30 dragon lizard species found in Australia.
The 12 species of seagrass in Shark Bay make it one of the most diverse seagrass assemblages in the world. Seagrass covers over 4 000 square kilometres of the bay, with the 1 030 square kilometre Wooramel Seagrass Bank being the largest structure of its type in the world.
Seagrass has contributed significantly to the evolution of Shark Bay as it has modified the physical, chemical and biological environment as well as the geology and has led to the development of major marine features, such as Faure Sill.
The barrier banks associated with the growth of seagrass over the last 5 000 years has, with low rainfall, high evaporation and low tidal flushing, produced the hypersaline Hamelin Pool and Lharidon Bight. This hypersaline condition is conducive to the growth of cyanobacteria which trap and bind sediment to produce a variety of mats and structures including stromatolites.
Stromatolites represent the oldest form of life on earth. They are representative of life-forms some 3 500 million years ago. Hamelin Pool contains the most diverse and abundant examples of stromatolite forms in the world.
Shark Bay is renowned for its marine fauna. The population of about 10 000 dugong, for example, is one of the largest in the world, and dolphins abound, particularly at Monkey Mia.
Humpback whales use the Bay as a staging post in their migration along the coast. This species was reduced by past exploitation from an estimated population of 20 000 on the west coast to 500-800 whales in 1962; the population is now estimated at 2 000-3 000.
Green and loggerhead turtles are found in Shark Bay near their southern limits, nesting on the beaches of Dirk Hartog Island and Peron Peninsula. Dirk Hartog Island is the most important nesting site for loggerhead turtles in Western Australia.
Shark Bay is also an important nursery ground for larval stages of crustaceans, fishes and medusae.
The Western Australian Government is responsible for day-to-day management of the Shark Bay World Heritage Area. |
